1. Field of the Invention
The present invention relates to a method and an apparatus for measuring a lead on a piece of apparatus, for example, a lead on a drum used to record a signal on a tape and/or to reproduce the signal from the tape.
2. Description of the Prior Art
Currently, approximately 100 different sorts of drums including drums used in consumer VTRs (video tape recorders) as well as non-consumer type VTRs, are available.
As to the drums, there has been proposed a lead measuring method for measuring the shape of the lead fabricated on the drum (e.g., the lower drum) on the basis of this drum per se, and also the lead measuring method for measuring the shape of the lead on the basis of the rotation shaft of the drum which has been assembled with respect to the rotation shaft of the drum. In addition thereto, the theoretical values for the variation amounts (.pi..times.drum diameter "D".times.tan lead ".theta.") of the respective lead shapes are different from each other with regard to 100 sorts of drums, so that the positions along the upper and lower direction would be changed.
Under such circumstances, every time the measuring method is changed and also the sort of drums to be measured is changed, the dedicated measuring machines must be specially manufactured in order to measure such different shapes of the leads formed on the drums.
There is another problem in case of manufacturing of such an dedicated measuring machine that this measuring machine should have either a dedicated copying (profiling) plane, or an exclusively-used copying (profiling) means. The copying plane, or means has a shape approximated to, for example, the theoretical value of the lead's shape.